Method of producing glucofrangulin of technical purity

ABSTRACT

Alder buckthorn bark (Rhamnus Frangula, Rhamnacae or Cortex Rhamnacae, Rhamni Frangulae), after prolonged drying in the usual manner, is treated with a water-alcohol mixture to form a raw extract from which heavy water-soluble impurities are removed. The resulting prepurified extract is, in turn, extracted with a solvent system of butanol or a higher alcohol and of water. The two-phase mixture is designed to solubilize the glucofrangulin in both phases.

United States Patent [191 Buchner et al.

[451 Dec. 17, 1974 METHOD OF PRODUCING GLUCOFRANGULIN OF TECHNICAL PURITY Inventors: Stanislaus Buchner, Birsfelden; Dragica Fischer, Basel, both of Switzerland Assignee: Solco Basel AG, Basel, Switzerland Filed: July 12, 1971 Appl. No.: 161,524

Foreign Application Priority Data July 13, 1970 Luxembourg 61323 June 22, 1971 Luxembourg 63400 US. Cl 260/210 F, 260/209 R Int. Cl. C076 47/18 Field of Search 260/210 F, 209

References Cited UNITED STATES PATENTS 8/1947 Griffin 260/210 F 2,534,250 12/1950 Eds et a1 260/210 F 2,662,893 12/1953 Kurth v 260/210 F 2,952,674 9/1960 Merritt et al.... 260/210 F 3,157,584 11/1964 Pouchet 260/210 F OTHER PUBLICATIONS Longo et al., Arch. Pharm., Vol. 297, pp. 248-251, 1964.

Primary Examiner-Johnnie R. Brown Attorney, Agent, or FirmWenderoth, Lind & Ponack [5 7] ABSTRACT 5 Claims, 1 Drawing Figure METHOD OF PRODUCING GLUCOFRANGULIN OF TECHNICAL PURITY FIELD OF THE INVENTION Our present invention relates to the recovery of glucofrangulin of technical purity from alder buckthorn bark and, more particularly, to the recovery of glucofrangulin in a higher state of purity than has been possible heretofore, at low cost.

BACKGROUND OF THE INVENTION It is known that glucofrangulin (C H O can be recovered as a pharmaceutically active medicinal from the bark of the alder buckthorn (Rhamnus frangula, Rhamnacae or Cortex Rhamni frangulae). The compound, which is thought to be obtained in two forms which appear to be isomers, is known to have laxative properties. The recovery of the active principle of the bark of the alder buckthorn and the pharmaceutical or medicinal properties thereof has been described in the literature, see for example:

Casparis, Maeder, Bull. Soc. Chim. Biol. 9, 324 (1927); Cucu, Jarpo, Pharmazie 14, 316 (1959); Knap et al., Czech par. 110,024 (1964); CA. 61, 41592 (1964). Schindler, Helv. Chim. Acta 29, 411 (1946); Horhammer et a1., Naturwiss. 51, 310 (1964); Longo et al., Arch. Pharm. 297, 248 (1964); Wagner, Horhammer, Nuturwiss. 53, 585 (1966).

For example, it is a common practice to process the bark of the alder buckthorn after the latter has dried for a substantial length of time, e.g. a year, to prevent any undue influence from fermenting green-cell growth and to dry the bark. The dried bark, stored for long periods and/or briefly heated in lieu of storage, is extracted in a finely ground state to produce a glucofrangulin containing extract which is therapeutically effective, e.g. as a laxative, in the manner already described. However, this extract may have varying concentrations of the active principle and it has been difficult to obtain a fixed concentration of the glucofrangulin in the extract or to recover the glucofragulin in a state of higher purity.

Among the methods suggested for purifying the extract, to recover the glucofrangulin in a state of increased purity or concentration, or to obtain the glucofrangulin in a more useful state, have been ionexchange, paper-chromatographic, column separation and thin-layer chromatographic techniques. In addition, it has been proposed to use precipitation methods in which lead acetate is added to the extract and to convert the glucofrangulin into an acetate salt which is purified. All of these methods have been time-consuming and laborious, so that they have not been suitable for industrial-level or commercial use.

OBJECT OF THE INVENTION It is the principal object of the present invention to provide an improved process for recovering glucofrangulin of high technical purity and utility from the bark of the alderbuckthorn, the method being economical and capable of being practiced on a commercial or in-' dustrial scale.

SUMMARY OF THE INVENTION We have discovered that this object and others which will become apparent hereinafter can be attained and a commercial process for producing glucofrangulin on an industrial scale with at least technical purity can be provided when the extraction process includes the step of treating a prepurified raw extract containing the glucofrangulin with a binary solvent consisting of butanol or a higheraliphatic alcohol and water, or with another binary or two-phase solvent system, in both phases of which glucofrangulin is soluble. In other words, although extracting sytems have been used heretofore, they have not proven to be successful on a commercial level, whereas the two-phase or binary solvent system described immediately above has enabled the glucofrangulin to be recovered substantially to the exclusion of other impurities and permits the glucofrangulin to be concentrated to any desired level or even recovered from the solvent system without the adverse influences of other components of the basic extract which have in the past interfered with glucofrangulin recovery.

According to another feature of the invention, the prepurified raw-bark extract is treated with the binary solvent mixture, constituted as described above, in a multilevel countercurrent liquid-liquid distribution column, so that the extraction is carried out in a plurality of stages in a countercurrent mode. The liquid can be introduced into the multistage arrangement continuously or discontinuously (intermittently) and the solvent phase can be introduced uniformly into all of the stages or can be injected therein impulsively. The solvent phase may also be transferred from stage to stage in bulk. Alternatively, the extraction may be carried out in successive stages, each of which uses a separate vessel, the solvent phase being transferred in bulk from vessel to vessel.

The binary solvent system used for extracting the raw extract preferably consists of two phases including an alcohol-saturated aqeuous phase and a water-saturated alcohol phase. In particular, one phase consists of butanol saturated with water while the other phase consists of water saturated with butanol. The distribution coefficient, defining the partition of glucofrangulin between the phases of the binary solvent system, is found to be dependent upon the pH of the solution, the ionic concentration and the concentration of the glucofrangulin extract. The recovery of the glucofrangulin, however, will depend also upon the volume ratio of the extracting solvent system to the raw extract where all other pa rameters, as indicated above, are held constant.

Investigations have shown that the distribution of the glucofrangulin of the prepurified raw extract is dependent upon the pH value of the aqueous phase, in the sense that at certain pH values the organically soluble glucofrangulin fraction is greater than with other pH values. Thus we can control the partition of the glucofrangulin between the phases and the concentration of the glucofrangulin in one or the other phase by regulating the pH value of the aqueous phase. We need only adjust the pH value to increase the glucofrangulin concentration in, for example, the organic phase to a desired level, should this level be unattained in the extraction process. Advantageously, control of the pH value is effected by adding a buffering system to the aqueous phase.

We mention, moreover, that any contact of water with the ground bark or the raw extract may lead to deterioration of the glucofrangulin if unduly prolonged. Hence, we prefer to carry outall of the steps in which water is in contact with the bark or the raw extract with immediacy to the point that there is no extended delay and successive procedures follow one another immediately.

Advantageously, the control of the pH is effected by the selective use of buffering substances, preferably phosphate buffers and the buffering system consisting of citric acid and disodiumhydrogenphosphate. It has been found that an optimum recovery of the glucofrangulin from the bark and from the raw extract may be had by providng a multistep process. In a first stage of the process, therefore, a water-extract system is passed countercurrent to the butanol at a pH promoting the transfer of the glucofrangulin from the aqueous phase to the butanol phase. The successive stage strips the glucofrangulin from the alcohol phase by passing it countercurrent to an aqueous phase of a pH of about 4 and sufficient to induce a transfer of glucofrangulin to this buffered aqueous phase. The glucofrangulin can then be recovered from the latter aqeuous phase and at a higher pH of,'say, 6.5, a fresh aqueous phase can be used to treat the butanol. It has been found that for preferential transfer of the glucofrangulin to the aqueous phase, a pH of about 4 is desirable while a preferential transfer to the butanol phase requires a pH of about 5.5. The precise pH can be determined by simple experience. In the final treatment stage, in which the glucofrangulin remains in the butanol'but impurities are removed, the pH should be about 6.5.

It should be noted that the principal impurities, removed in major part during the prepurification, are the glucofrangulin decomposition products frangulin and emodin. For a further purification to remove these components, we may make use of a second extraction with methylene chloride or a like organic solvent which is is capable of selective separation of glucofrangulin from frangulin and emodin. The use of the methylene chloride is considered part of the prepurification for the purposes of the present invention and preferably is carried out continuously with a proportion of 10 liters of methylene chloride per kg of the frangular raw extract at a temperature of 20- 35 C. This treatment is best effected after the water treatment mentioned earlier. The final controlled-pH extraction, of course, removes any residual impurities and even the limited quantities of emodin and frangulin remaining.

Prior to the prepurification' treatment, the bark is stored over a long period, preferably at least a year, and/or is heated for at least an hour to a temperature of lO C. These conditions are sufficient to oxidize the antranol to anthroaquinone which is removed in the subsequent purification stages. The bark is ground, preferably in a dry state, to a particle size between 100p and 150; before the initial extraction. The raw extract is obtained by treating the finely ground bark with a water-alcohol system containing water and alcohol in a volume ratio of 1:9 to 9:1 at a temperature between 20 and 70 C using a total of to liters of the system per kg of bark. Preferably the mixture consists of water and methanol in a volume ratio of l:9. The pH during treatment should range between the weakly acid and neutral, e.g. betweeh pH 7 and pH 5. Extraction is carried out under these conditions until, by analysis of the extract, no more glucofrangulin is removed.

The extract is then converted into the frangula raw extract by vacuum evaporation at a temperature of 18 C and a pressure of 20 mm Hg or below until the extract has a syrupy consistency. The initial extract may make use of ethanol and isopropanol in addition to or in place of methanol.

The initial purification is effected by adding water to the raw extract, preferably in an amount of 2 4 liter/kg of the bark originally treated. The addition of water is terminated when precipitation from the extract terminates.

After the water prepurification we prefer, as described earlier, to treat the raw extract with an organic solvent such as methylene chloride. In addition to methylene chloride, the following solvents have been found to be satifactory individually or in combination: ethylene chloride, ethyl ether, chloroform, petroleum ether and benzene.

The two-phase higher-alcohol/water system for recovery of the glucofrangulin of technical purity may include, as the organic phase, normal-butanol, isobutanol, secondary-butanol, tertiary butanol, amylalcohol, isoamyl alcohol, methylethylketone and methylisobutylketone or mixtures thereof. The water: organic phase volume ratio should range between 1:3 and 3: l. The glucofrangulin may be recovered by evaporation in vacuo at a temperature of 20 to 50 C. The recovered glucofrangulin can be purified by precipitation from absolute alcohol.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing, the sole FIGURE of which is a flow diagram illustrating a specific Example to be described in greater detail hereinaf ter.

SPECIFIC DESCRIPTION In the drawing, we show an extraction setup, consisting of ten extracting columns I X, the functions of which are described below in Example Ill. The column 10 receives, at the lower end, the alcohol or ketone component of the two-phase final solvent system via an inlet 12 from a peristaltic pump, 11, the organic phase (e.g. butanol) passing upwardly through the column and being recovered at 13; thence it is fed by a peristaltic pump 14 and a line 15 tothe bottom of the next extraction column 16. In a similar manner, the butanol phase is advanced by pumps 17, 21, 24, 27, 30, 32,35 and 37 and lines 18, 20, 23, 26, 29, 33, 72 and 38 to and through the columns 16, 19, 22, 25, 28, 31', 34, 36 and 39 in succession.

From column 39, the butanol phase is led via line 40 and a pump 41 to a still 42 in which the solvent is recovered and delivered via line 44 to the inlet of the system at pump 1 l. The residue is collected at 43 and fed via a line 47 together with raw extract (line 49) and a buffered aqueous phase of pH 5.5 to a peristaltic pump 45 supplying the column 22 at the top via line 46.

The path of the aqueous phase is shown in a broken line in the drawing and traverses the columns 22, l9, l6 and 10 countercurrent to the butanol phase and is advanced by the peristaltic pumps 51, 53 and via lines 50, 52 and 71. The aqueous phase, stripped of the glucofrangulin, is discharged for disposal at 54.

A second aqueous phase, buffered to a pH of about 4, traverses the columns 34, 31, 28 and 25 in counterflow to the butanol and is advanced through these columns via lines 55, 57, 73 and 6l with peristaltic pumps 56, 58, 59 and 60. The glucofrangulin is recovered from the aqueous phase at 62 in the form of a powder 63.

A third aqueous phase is fed to the column 39 by a pump 64 and a line 65 and is passed via line 66 and a pump 67 into column 36 from which the aqueous phase is eliminated at 68.

SPECIFIC EXAMPLES EXAMPLE I resulting suspension. The filtrate was collected and the ground bark removed from the filter, pressed and returned for further extraction. The pH of the suspension was held at 6.5. The extraction process was continued as long as a chromatographic test of a sample of each extraction filtrate showed the presence of glucofrangulin. As soon as the test became negative, extraction was discontinued.

The collected filtrate from all of the extraction steps was evaporated under vacuum at a temperature of 50 C at mm Hg pressure to a syrup-like consistency. This syrup is the frangula raw extract serving as the precursor for the prepurified raw extract.

The frangula raw extract is then treated with water in an amount sufficient to completely drive out impurities. A preferred ratio of the water to the extract corresponded to 4 liters of water per kg of treated ground bark. Additional water results in no further precipitation of impurities. The impurities which precipitate are denatured albumins and tannin or tannin-like substances, resins and other impurities of low solubility in water. The solution which is decanted and filtered free from the impurities is rich in glucofrangulin and also contains other impurities. The filtrate is, in turn, concentrated by evaporation in vacuo at a temperature of 50 C and a pressure of 20 mm Hg to produce prepurified raw extract.

The liquid-liquid distribution of the prepurified raw extract is carried out in a multistage extractor by passing the raw extract phase countercurrent to the binary solvent phase which consists of butanol and water in a volume ratio of 111 until the glucofrangulin is recovered with technical purity in the butanol-water extract. The residue contains the remaining impurities. Preferably, the liquid-liquid distribution is carried out in a Craig extractor. Recovery of the glucofrangulin is effected by evaporating the butanol-water mixture to dryness at a temperature of 50 C and at a pressure of 20 mm Hg. Other liquid-liquid contactors have also been found to be suitable, including the countercurrent cascade described at page 21 of PERRYS CHEM- ICAL ENGINEERS HANDBOOK, McGraw-Hill Book Co., 1964. A

The process between the initial treatment of the bark with the methanol-water solution to the recovery of the initial frangular extract can be carried out over a period of 48 hours with the stages immediately following one another. From the moment that this raw extract is treated with water in a prepurification stage, the process must proceed with immediacy and without any delay. The alder-buckthorn bark was found to contain about 7 percent by weight glucofrangulin which was percent (by weight) recovered. The product from the evaporation of the final extract to dryness, was pulverulent glucofragulin of technical purity.

EXAMPLE II Example I was followed except that prior to treatment of the water-rectified raw extract with the butanol-water system, the prepurified extract was addiionally treated with 10 liters of methylene chloride per kg of the raw extract at a temperature of about 30 C. The methylene-chloride phase is found to contain the major part of the impurities remaining after the prepurification with water. The methylene-chloride phase is then recovered and evaporated in a solvent recovery process to distil off the methylene chloride which is condensed and reused. The distillation can precede or be concurrent with the concentration of the prepurified filtrate. Thus we prefer to carry out the elimination of methylene chloride and the concentration of the solution at a temperature of 50 C under a reduced pressure of 20 mm Hg until a syrup-like density is again obtained. The twice prepurified raw extract is then subjected to multistage extraction as described in connection with Example I to recover technically pure glucofrangulin.

EXAMPLE III The prepurified water-treated raw extract is obtained as described in Example I. This raw extract is then immediately treated with the two-phase solvent of butanol and water in countercurrent to transfer the glucofrangulin with technical purity to the solventsystem and permit the glucofrangulin to be recovered in a powdered form upon drying of the solvent system. The multistage distribution is carried out in an extraction battery having ten columns according to the system of R0- metsch (E. I-Iecker: VERTEILUNGSVERFAHREN IM LABORATORIUM, Verlag Chemie, Weinheim, 1955, S. 128). In such an extractor or contactor, each column is constituted as a cylindrical upright vessel which is subdivided into upper and lower baffle sections and having a contacting zone between them. The individual sections are not separated from one another so that fluid within one column can flow from one section to another. The outer vessel has a circular crosssection and a diameter of mm, while the individual baffle sections each extend over 400 mm and are separated by a contact zone running over 800 mm. Baffle disks and agitators or stirrers are also provided. In all 10 of the columns, the aqueous phase is fed through an upper end of the corresponding contacting zone while the butanol phase is introduced through fittings at the other end of the contacting zone. The butanol phase is recovered at an upper end of the vessel and the aqueous phase is recovered at a lower end thereof. The flow of the aqueous and butanol phases is produced by peristaltic pumps provided in the connecting pipes of the system. The 10 columns, designates I, II X, are so connected together that the butanol phase passes through the columns in this succession, i.e., is introduced initially into column I, traverses the latter, and is then introduced into column II, etc. until it is recovered at column X. The aqueous phase follows in countercurrent to the butanol phase. The butanol phase is supplied with a volume rate of flow of liter/hour and traverses the system at this rate.

The aqueous phase, buffered with a phosphate solution to a pH of 6.5, is fed into column X at a rate of 3 liter/hour and is discharged immediately upon traversing this stage and column IX, since it is highly impure. In column VIII, a fresh aqueous phase is supplied at a rate of liter/hour, buffered with a phosphate buffer solution to a pH of 4. This aqueous phase flows countercurrent to the butanol through columns VII V and then is completely removed. In column V, which constitutes the glucofrangulin recovery stage, the aqueous phase contains the isolated glucofrangulin. In column IV a fresh aqueous phase buffered to a pH of 5.5 with a phosphate buffer, is introduced at a rate of 2 liter/- hour. The buffer solutions in all cases are constituted by solutions of disodiurnhydrogen phosphate and citric acid in appropriate concentrations.

Twenty-five percent by weight of the prepurified raw extract (Example I) is dissolved in the aqueous phase which is introduced into column IV and is carried with the aqueous phase (pH 5.5) through the columns III to I. The aqueous phase is then discarded. In columns I 4 IV, because of the pH value of 5.5, the glucofrangulin is transferred to the butanol phase. in columns V to VII] the glucofrangulin preferentially is taken up by the aqueous phase because of the pH of 4. The glugofrangulin is thus recovered from the water in the recovery stage. In columns IX and X, the glucofrangulin preferentially is transferred into the butanol phase because the pH is at 6.5 and is discharged from the system. The glucofrangulin of this butanol phase may be combined with that of columns I IV to recover residual glucofrangulin. Where the pH is 5 or greater, transfer is preferably to the organic phase; where the pH is below 5, the transfer is predominantly to the water phase.

In columns I IV, the volume ratio of aqueous phase: butanol phase is 2:5 to promote preferential transfer of the glucofrangulin to the butanol phase. In columns V to VIII, the volume ratio of the aqueous phase to the butanol phase is 10:5 to promote transfer of the glucofrangulin to the aqueous phase. In columns IX and X, the volume ratio of the aqueous phase to the butanol phase is 3:5.

The aqueous phase recovered from column V is evaporated in vacuo mm Hg) at 50 C to dryness. The residue is powdered glucofrangulin of technical purity. The glucofrangulin may be further purified by crystallization or precipitation from absolute ethanol. The product is 95 percent (by weight) glucofrangulin.

EXAMPLE IV Glucofrangulin, produced as described in Example III is used to treat human constipation in daily single doses of 24 to 36 mg.

EXAMPLE V Glucofrangulin, as made in Example III, is put up in l percent and 5 percent ethanol solutions and is used to treat the mucous tissues of the nose and throat. The solution is administered by spraying or gargling and both solutions are found to be suitable for treatment of gum inflammations. There are no noticeable adverse reactions.

We claim:

1. A continuous method for producing technically pure glucofrangulin from an aqueous alcoholic raw extract of alder buckthorn bark containing impurities comprising frangulin and emodin which consists essentially of the steps of:

a. precipitating impurities poorly soluble in water from said raw extract by treating it with water;

b. removing said impurities poorly soluble in water by filtration to produce a prepurified glucofrangulin containing raw extract;

c. subjecting said prepurified raw extract to countercurrent liquid-liquid extraction with a binary solvent system consisting of 1) an organic phase consisting of water-saturated butanol or higher aliphatic alcohol, methyl ethyl ketone, methylisobutyl ketone or water saturated mixture thereof and (2) an aqueous phase saturated with the organic phase adjusted to a pH of about 5.5, to effect preferential transfer of said glucofrangulin into said organic phase;

d. countercurrently contacting the thus obtained glucofrangulin-containing organic phase from step (c) with an aqueous phase adjusted to a pH of about 4 to effect preferential transfer of glucofrangulin from said organic phase into said aqueous phase;

e. evaporating said glucofrangulin-containing aqueous phase from step (d) to recover glucofrangulin of technical purity;

f. countercurrently contacting the organic phase from step (d) with an aqueous phase adjusted to pH of about 6.5 or above, to effect preferential transfer of impurities into said aqueous phase with retention of glucofrangulin in said organic phase;

g. discarding said aqueous phase from step (f);

h. evaporating said organic phase from step (f) to recover organic solvent therefrom, thereby producing a residue containing glucofrangulin, emodin and frangulin and i. adding said residue of step (h) along with a new portion of prepurified raw extract to step (c).

2. A method as claimed in claim 1 wherein said prepurified raw extract is further purified after step (b) and before step (c) by treating it with methylene chloride, ethylene chloride, ethyl ether, chloroform, petroleum ether or benzene.

3. A method as claimed in claim 1 wherein the recovered organic solvent from step (h) is returned to step (c).

4. A method as claimed in claim 1 wherein the pH is adjusted in steps (c), (d) and (f) by a buffer.

5. A method according to claim 1 wherein the organic solvent is butanol. 

1. A CONTINUOUS METHOD FOR PRODUCING TECHNICALY PURE GLUCOFRANGULIN FROM AN AQUEOUS ALCOHOLIC RAW EXTRACT OF ALDER BUCKTHORN BARK CONTAINING IMPURITIES COMPRISING FRANGULIN AND EMODIN WHICH CONSISTS ESSENTIALLY OF THE STEPS OF: A. PRECIPITATING IMPURITIES POORLY SOLUBLE IN WATER FROM SAID RAW EXTRACT BY TREATING IT WITH WATER; B. REMOVING SAID IMPURITIES POORLY SOLUBLE IN WATER BY FILTRATION TO PRODUCE A PREPURIFIED GLUCOFRANGULIN CONTAINING RAW EXTRACT; C. SUBJECTING SAID PREPURIFIED RAW EXTRACT TO COUNTERCURRENT LIQUID-LIQUID EXTRACTION WITH A BINARY SOLVENT SYSTEM CONSISTING OF (1) AN ORGANIC PHASE CONSISTING OF WATERSATURATED BUTANOL OR HIGHER ALIPHATIC ALCOHOL, METHYL ETHYL KETONE, METHYLISOBUTYL KETONE OR WATER SATURATED MIXTURE THEREOF AND (2) AN AQUEOUS PHASE SATURATED WITH THE ORGANIC PHASE ADJUSTED TO A PH OF ABOUT 5.5, TO EFFECT PREFERENTIAL TRANSFER OF SAID GLUCOFRANGULIN INTO SAID ORGANIC PHASE; D. COUNTERCURRENTLY CONTACTING THE THUS OBTAINED GLUCOFRANGULIN-CONTAINING ORGANIC PHASE FROM STEP (C) WITH AN AQUEOUS PHASE ADJUSTED TO A PH OF ABOUT 4 TO EFFECT PREFERENTIAL TRANSFER OF GLUCOFRANGULIN FROM SAID ORGANIC PHASE INTO SAID AQUEOUS PHASE; E. EVAPORATING SAID GLUCOFRANGULIN-CONTAINING AQUEOUS PHASE FROM STEP (D) TO RECOVER GLUCOFRANGULIN OF TECHNICAL PURITY; F. COUNTERCURRENTLY CONTACTING THE ORGANIC PHASE FROM STEP (D) WITH AN AQUEOUS PHASE ADJUSTED TO PH ABOUT 6.5 OR ABOVE, TO EFFECT PREFERENTIAL TRANSFER OF IMPURITIES INTO SAID AQUEOUS PHASE WITH RETENTION OF GLUCOFRANGULIN IN SAID ORGANIC PHASE; G. DISCARDING SAID AQUEOUS PHASE FROM STEP (F); H. EVAPORATING SAID ORGANIC PHASE FROM STEP (F) TO RECOVER ORGANIC SOLVENT THEREFROM, THEREBY PRODUCING A RESIDUECONTAINING GLUCOFRANGULIN, EMODIN AND FRANGULIN AND I. ADDING SAID RESIDUE OF STEP (H) ALONG WITH A NEW PORTION OF PREPURIFIED RAW EXTRACT TO STEP (C).
 2. A method as claimed in claim 1 wherein said prepurified raw extract is further purified after step (b) and before step (c) by treating it with methylene chloride, ethylene chloride, ethyl ether, chloroform, petroleum ether or benzene.
 3. A method as claimed in claim 1 wherein the recovered organic solvent from step (h) is returned to step (c).
 4. A method as claimed in claim 1 wherein the pH is adjusted in steps (c), (d) and (f) by a buffer.
 5. A method according to claim 1 wherein the organic solvent is butanol. 